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  • Pathology literally means the study (logos) of suffering (pathos)
  • Pathology is the study of the structural, biochemical & functional changes in cells, tissues & organs that underlie disease
  • By the use of molecular, microbiologic, immunologic & morphologic techniques, pathology attempts to explain the whys and wherefores of the signs and symptoms manifested by patients while providing a rational basis for clinical care & therapy
  • It is thus a bridging discipline involving both basic sciences & clinical practice
  • It is also the scientific foundation for all medicine


  • Traditionally, the study of pathology is divided into;
    • General pathology &
    • Systemic pathology

General Pathology

  • General pathology is concerned with the common reactions of cells & tissues to injurious stimuli
  • Such reactions are often not tissue specific
  • Acute inflammation in response to bacterial infections produces a very similar reaction in most tissues

Systemic Pathology

  • Systemic pathology, on the other hand, examines the alterations and underlying mechanisms in organ specific diseases such as ischaemic heart disease


  • There are 4 aspects of a disease process that from the core of pathology:
    • Its cause (etiology)
    • The biochemical & molecular mechanisms of its development (pathogenesis)
    • The structural alterations induced in the cells & organs of the body

(morphological changes), &

  • The functional consequences of these changes (clinical manifestations)


  • The initiating cause of a disease
  • Can be genetic or acquired


Genetic and environmental factors may combine to produce a diseases state e.g. hypertension, diabetes mellitus (DM), asthma, cancers and schizophrenia

Please NOTE;

  • One causative agent may be responsible for specific diseases e.g. leprosy and M. leprae  Several aetiological agents may produce specific disease e.g. ü Meningitis – E. coli, H. influenzae, Pneumococcus
    • Lobar pneumonia – pneumococcus, staphylococcus
    • Lung abscess – Staphylococcus bacteriodes
  • Some causative agents may produce structural/morphological changes that are specific  Several diseases have unknown aetiology e.g.
    • Crohn’s disease
    • Ulcerative colitis ü Sarcoidosis, etc.


  • Refers to the sequence of cellular, biochemical and molecular events that follow the exposure of cells or tissues to an injurious agent
  • Explains how the underlying aetiologies produce the morphologic & clinical manifestations of the disease
  • Remains one of the main domains of Pathology
  • Even when the initial cause is known, it is many steps removed from the expression of the disease

Morphological Changes

  • Refers to the structural alterations in cells or tissues
  • Can be unique and specific and therefore characteristic of the disease or diagnostic of the aetiological agent
  • Some are visible to the naked eyes and are called GROSS CHANGES
  • Others are visible only with the aid of light microscope and are called


  • Others require electron/scanning electron microscopes and are referred to as


Functional Derangements & Clinical Manifestations

  • The end results of genetic, biochemical and structural changes in cells and tissues are functional abnormalities
  • These lead to the clinical manifestations (symptoms and signs) of disease, as well as its progress (clinical course and outcome)
  • Hence, clinicopathologic correlations are very important in the study of disease

Summary: Cell Pathology